Casting apparatus whose cooling flow passage is formed by welding and method for manufacturing the same

ABSTRACT

A casting apparatus for manufacturing a cast product from molten metal includes a molten metal and a cooling portion. The molten metal contacts a surface for contact with the molten metal. The cooling portion forms a cooling flow passage. The cooling flow passage is configured to cool the molten metal contacting surface. At least a part of an inner surface of the cooling flow passage is constituted of a welding portion formed by welding, the welding portion sealing the cooling flow passage. The welding portion is constituted such that an exposure to the molten metal becomes equal to or less than a predetermined ratio with respect to an area of the welding portion constituting the inner surface of the cooling flow passage.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority from Japanese Patent Application No.2014-210324 filed with the Japan Patent Office on Oct. 14, 2014, theentire content of which is hereby incorporated by reference.

BACKGROUND

1. Technical Field

The present invention relates to a casting apparatus, such as a mold anda sprue bushing, used for die-cast casting or a similar casting and amethod for manufacturing the casting apparatus. More specifically, thepresent invention relates to the casting apparatus that internallyincludes cooling flow passages for cooling the casting apparatus and themethod for manufacturing the casting apparatus.

2. Related Art

Conventionally, build-up welding has been performed to repair molds, andthere has been proposed an improvement of the method (for example,Japanese Unexamined Patent Application Publication No. 2011-115807). Inmanufacturing the molds as well, to expand a freedom of design forforming a flow passage, the manufacturing method using the build-upwelding has been proposed (for example, Japanese Unexamined PatentApplication Publication No. 2004-34133, Japanese Unexamined PatentApplication Publication No. H05-309468, and Japanese Unexamined PatentApplication Publication No. 2005-52892). Meanwhile, a spread ofwater-soluble mold release agent for die-casting or a similar agentallows rapidly cooling the molds. While shortening of a manufacturingcycle is achieved, a problem of a heat check and a crack is likely tooccur. Furthermore, it has been known as technical common knowledge thatthe welding repair is one cause of reduction in mold life (“Measures ForService Life Of Mold For Die-Casting”, written by Masahiko Hihara,published by NIKKAN KOGYO SHIMBUN, LTD., Feb. 28, 2003, p. 289). Theintroduction of a cooling flow passage has been proposed also for thecasting apparatus other than the mold such as the sprue bushing(Japanese Unexamined Patent Application Publication No. 2003-10953).

However, while a welding process is suitable for manufacturing thecooling flow passage, which is required to feature air tightness, fromthe aspect of durability of the casting apparatus, sufficientexamination has been required to the welding process.

SUMMARY

One or more embodiments provide a casting apparatus manufactured usingthe welding process for manufacturing the cooling flow passages whileminimizing deterioration of durability of the casting apparatus and amethod for manufacturing the casting apparatus.

One or more embodiments of the present invention provides a castingapparatus for manufacturing cast products from molten metal. The castingapparatus includes a molten metal contacting surface and a coolingportion. The molten metal contacting surface is in contact with themolten metal. The cooling portion forms a cooling flow passage. Thecooling flow passage is configured to cool the molten metal contactingsurface. At least a part of an inner surface of the cooling flow passageis constituted of a welding portion formed by welding. The weldingportion seals the cooling flow passage. The welding portion isconstituted such that an exposure to the molten metal becomes equal toor less than a predetermined ratio with respect to an area of thewelding portion constituting the inner surface of the cooling flowpassage.

With the casting apparatus of one or more embodiments according to thepresent invention, at least a part of the inner surface of the coolingflow passage is constituted of the welding portion formed by welding.This allows minimizing excessive temperature rise by casting and alsoallows minimizing rapid temperature fall by cooling with a mold releaseagent. Meanwhile, the welding portion is constituted such that theexposure to the molten metal becomes equal to or less than thepredetermined ratio with respect to the area of the welding portionconstituting the inner surface of the cooling flow passage. This allowsminimizing an influence of fatigue degradation caused by a temperaturecycle by sufficient cooling. Consequently, the reduction in durabilityof the casting apparatus caused by the welding process can be minimized.The predetermined ratio can be set appropriately depending on theoperating state and the design of the casting apparatus.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a cross-sectional view illustrating a constitution of a mold100 according to a first embodiment of the present invention;

FIG. 2 is a flowchart illustrating a method for using the mold 100according to the first embodiment;

FIG. 3A is a process drawing illustrating the method for using the mold100 according to the first embodiment;

FIG. 3B is a process drawing illustrating the method for using the mold100 according to the first embodiment;

FIG. 3C is a process drawing illustrating the method for using the mold100 according to the first embodiment;

FIG. 4 is a flowchart illustrating a method for manufacturing the mold100 according to the first embodiment;

FIG. 5A is a process drawing illustrating the method for manufacturingthe mold 100 according to the first embodiment;

FIG. 5B is a process drawing illustrating the method for manufacturingthe mold 100 according to the first embodiment;

FIG. 5C is a process drawing illustrating the method for manufacturingthe mold 100 according to the first embodiment;

FIG. 6 is a cross-sectional view illustrating a constitution of adie-cast-casting-machine use spool bush 200 according a secondembodiment;

FIG. 7 is a flowchart illustrating a method for manufacturing the spoolbush 200 according to the second embodiment;

FIG. 8 is an exploded view illustrating the method for manufacturing thespool bush 200 according to the second embodiment;

FIG. 9 is a process drawing illustrating an assembled state (beforewelding) of a bush body 220 and an outer liner 230 according to thesecond embodiment;

FIG. 10A is a cross-sectional view illustrating a part of a constitutionof a mold 300 according to a third embodiment;

FIG. 10B is a process drawing illustrating a state after a machiningprocess (before welding) of the mold 300 according to the thirdembodiment; and

FIG. 11 is a flowchart illustrating the method for manufacturing themold 300 according to the third embodiment.

DETAILED DESCRIPTION

The following describes respective embodiments of the present inventionin the following order. It will be understood that the scope of thepresent invention is not limited to the described embodiments, unlessotherwise stated.

A. Constitution of Casting Apparatus (Mold) in First Embodiment: B.Method for Using Mold in First Embodiment: C. Method for ManufacturingMold in First Embodiment: D. Constitution of Casting Apparatus (SpoolBush) in Second Embodiment: E. Method for Manufacturing Spool Bush inSecond Embodiment: F. Constitution of Casting Apparatus (Mold) in ThirdEmbodiment: G. Method for Manufacturing Mold in Third Embodiment: H.Modification: A. Constitution of Casting Apparatus (Mold) in FirstEmbodiment

FIG. 1 is a cross-sectional view illustrating a constitution of a mold100 according to a first embodiment of the present invention. The mold100 includes an insert die 110, a fixed-side main mold 120, and amovable-side main mold 130. The insert die 110 has a product shapeforming surface 110 s, which forms the shape of a cast product. Thefixed-side main mold 120 has a product shape forming surface 120 s. Themovable-side main mold 130 has a product shape forming surface 130 s anda depressed portion 130 c. The three product shape forming surfaces 110s, 120 s, and 130 s can form an enclosed space for casting cast productsin a mold-set-up state, which will be described later. This enclosedspace will be described later. The mold 100 is the casting apparatusused for casting.

The insert die 110 includes a first part 111, a second part 112, and abolt 113. The first part 111 has the product shape forming surface 110s. The second part 112 has an outer surface fitted to the depressedportion 130 c of the movable-side main mold 130. The bolt 113permanently fastens the first part 111 and the second part 112. In thisembodiment, when viewed from the axial direction of the bolt 113, allthe three product shape forming surfaces 110 s, 120 s, and 130 s have acircular shape around its axial center. The product shape formingsurfaces 110 s, 120 s, and 130 s are also referred to as molten metalcontacting surfaces.

The product shape forming surface 110 s of the insert die 110 hasprotrusions 111 p. The protrusion 111 p is a shaping part disposed uponrequest of outer specification of cast products. Focusing on the shapeof the protrusion 111 p, the protrusion 111 p has a property of likelyto be a high temperature during a molten metal pouring process andlikely to be rapidly cooled during cooling. This is because that whilethe protrusion 111 p is surrounded by molten metal and cooling water, aheat conduction path to the movable-side main mold 130 is narrow.

The insert die 110 includes cooling water passages 114 (whichcorresponds to a cooling portion in the appended claims) to reduce theabove-described temperature change. The cooling water passage 114 has anannular, circulating shape viewed from the axial direction of the bolt113. The cooling water passage 114 communicates with a cooling waterinlet and a cooling water discharge port (not illustrated). The coolingwater passages 114 are formed by covering openings of the annulardepressed portions, which are formed at the first part 111, with thesecond part 112. The cooling water passage 114 is sealed from theoutside of the cooling water passage 114 with a weld bead 110 b (alsoreferred to as a welding portion or a weld-overlay portion), which joinsthe first part 111 and the second part 112.

The fixed-side main mold 120, the movable-side main mold 130, the firstpart 111, and the second part 112 are all made of an SKD 61 and/or othertool steels. The weld bead 110 b is a part over which deposited metalwith a composition similar to the SKD 61 is overlaid. This build-upwelding is formed by TIG welding using a TIG welding rod (for example,DS-61G). The combination of a plurality of components forms themovable-side main mold 130 and the insert die 110, thus constituting oneside of the mold 100.

The entire outer surface of the weld bead 110 b is in contact with theinner surface of the depressed portion 130 c of the movable-side mainmold 130. Thus, the mold 100 is constituted such that the weld bead 110b is not to be exposed to the molten metal. Since the weld bead 110 b isnot exposed to the molten metal, this allows preventing a heat cyclecaused by the contact of the weld bead 110 b with the molten metal.Furthermore, the entire outer surface of the weld bead 110 b is incontact with the movable-side main mold 130, this allows exchanging heatremarkably effective between the outer surface and the movable-side mainmold 130. Accordingly, partial excessive temperature change only at theouter surface of the weld bead 110 b can be minimized. This allowsminimizing a heat check and a crack.

B. Method for Using Mold in First Embodiment

FIG. 2 is a flowchart illustrating a method for using the mold 100according to the first embodiment. FIG. 3A to FIG. 3C are processdrawings illustrating the method for using the mold 100 according to thefirst embodiment. To produce cast products, the mold 100 is used in thefollowing method.

Step S11 performs a mold-setting-up process. The mold-setting-up processforms a mold with the fixed-side main mold 120 and the movable-side mainmold 130 from which the cast product has been taken out and where thecooling has been completed (see FIG. 3A). The mold-setting-up processmoves the movable-side main mold 130 having the insert die 110, andforms the enclosed space (see FIG. 3B). The enclosed space is to castthe cast products with the three product shape forming surfaces 110 s,120 s, and 130 s, which are provided to the fixed-side main mold 120,the insert die 110, and the movable-side main mold 130, respectively.

Step S12 performs the molten metal pouring process. The molten metalpouring process press-fits a high-temperature molten metal to the mold.As the molten metal, for example, an aluminum alloy is used. Thisheightens the temperatures of all the product shape forming surfaces 110s, 120 s, and 130 s. Meanwhile, the molten metal hardens and an aluminumdie-cast product (not illustrated) is casted. After completion ofsolidification, the process proceeds to the next process.

Step S13 performs a mold opening process. The mold opening process movesthe movable-side main mold 130 to separate the movable-side main mold130 from the fixed-side main mold 120 to allow extraction of thealuminum die-cast product (not illustrated). Step S14 extracts thealuminum die-cast product. Then, the manufacturing process for aluminumdie-cast products with the mold 100 is completed. The manufacturingprocess for aluminum die-cast products proceeds to the next process,which does not use the mold 100.

Step S15 applies a mold release agent to the insert die 110, thefixed-side main mold 120, and the movable-side main mold 130 with aspray device 190 (see FIG. 3C). This embodiment uses a water-solublemold release agent for die-casting (for example, TX-2400 and GL-3700) asthe mold release agent. The mold release agent is applied by sprayingthe water-soluble mold release agent for die-casting to the productshape forming surfaces 110 s, 120 s, and 130 s (see FIG. 3C). Aftercompletion of the cooling (Step S16), in the case where the aluminumdie-cast product is not an end product, the process can be returned tothe mold-setting-up process (Step S10) (Step S17). In the case where thealuminum die-cast product is the end product, the process is terminated.

The water-soluble mold release agent for die-casting formsmold-releasing films over the product shape forming surfaces 110 s, 120s, and 130 s. Meanwhile, evaporation of the water vapor allows theproduct shape forming surfaces 110 s, 120 s, and 130 s to be rapidlycooled. This allows achieving the short cycle time of the castingprocess.

The rapid cooling of the product shape forming surfaces 110 s, 120 s,and 130 s increases the problem of thermal fatigue, causing the heatcheck and the crack. Specifically, according to the knowledge of theinventor of this application, in a process where the product shapeforming surfaces 110 s, 120 s, and 130 s whose temperatures become highby the molten metal pouring process are rapidly cooled and contracted bythe evaporation of the water vapor of the water-soluble mold releaseagent for die-casting, the heat check and the crack occur. This isbecause that the rapid contraction of the surface generates a thermalexpansion difference between the surface part and the inner part,resulting in a strain.

In this embodiment, focusing on its shape, especially the protrusion 111p provided with the product shape forming surface 110 s, has a propertylikely to be a high temperature during the molten metal pouring process.This is because that while the protrusion 111 p is surrounded by themolten metal, the heat conduction path to the movable-side main mold 130is narrow. However, in this embodiment, since the cooling water passages114 are formed at the inside of the protrusions 111 p, this allowsminimizing the excessively high temperature of the protrusions 111 p.Furthermore, while the process continues from the molten metal pouringprocess (Step S12) to the mold opening process (Step S13) and thenproceeds to the application of the mold release agent (Step S15), theprotrusion 111 p can also be cooled with the cooling water passage 114.This allows effectively minimizing the heat check and the crack, whichare caused by the cooling by the application of the mold release agent.

In this embodiment, the cooling water passages 114 are sealed by theweld beads 110 b. With general technical common knowledge, it isconsidered that a mold life of a part of a die-casting mold where thewelding repair has been performed is remarkably reduced compared with anon-welded portion (for example, Measures For Service Life Of Mold ForDie-Casting, written by Masahiko Hihara, NIKKAN KOGYO SHIMBUN, LTD.).However, in this embodiment, it is less likely that the weld bead 110 bcauses the reduction in mold life at least due to the following reasons.The other reasons will be described later.

(1) Since the weld bead 110 b seals the cooling water passage 114, theweld bead 110 b is not in an excessively high temperature state.(2) The weld bead 110 b does not form the product shape forming surface110 s (not exposed to the enclosed space (see FIG. 3B), which is to castthe cast product). Accordingly, the weld bead 110 b does not become ahigh temperature excessively and is not exposed under a rapidtemperature decrease, which is caused by application of the mold releaseagent.(3) The weld bead 110 b is in contact with the movable-side main mold130. Accordingly, the weld bead 110 b and the movable-side main mold 130do not form a thermal boundary and do not generate excessively largeheat gradient.

Accordingly, the mold 100 having the constitution of the firstembodiment uses the welding process for manufacturing a cooling flowpassage 140 while minimizing the deterioration of durability of the mold100. This achieves the appropriate cooling flow passage, ensuringachieving the mold 100 having long life.

C. Method for Manufacturing Mold in First Embodiment

FIG. 4 is a flowchart illustrating the method for manufacturing the mold100 according to the first embodiment. FIG. 5A to FIG. 5C are processdrawings illustrating the method for manufacturing the mold 100according to the first embodiment. To achieve the above-describedconstitution, the mold 100 is manufactured by the following method. StepS21 performs the machining process on the respective components (seeFIG. 5A). Especially, the respective components of the first part 111and the second part 112, which constitute the insert die 110, are allmanufactured by performing the machining process on materials, which isthe SKD 61, before quenching.

On the outer periphery of the first part 111, depressed portions 111 w,which have a depressed shape for build-up welding, are formed. On theouter periphery of the second part 112, depressed portions 112 w, whichhave a depressed shape for build-up welding, are formed.

Step S22 assembles the respective components. Specifically, the firstpart 111 and the second part 112, which constitute the insert die 110,are combined. The combined first part 111 and second part 112 arefastened by the bolt 113. This forms the depressed portions 111 w and112 w (see FIG. 5B) to form the weld beads 110 b across the peripheralareas of the first part 111 and the second part 112. The depressedportions 111 w and 112 w have a semicircular cross section.

Step S23 performs the welding process. As described above, the weldingprocess is performed by forming the weld bead 110 b (see FIG. 1 and FIG.5C) by the TIG welding using the TIG welding rod (for example, theDS-61G). The weld bead 110 b is appropriately melted into both the firstpart 111 and the second part 112, thus constituting a gradient metal.

Note that the TIG welding rod (for example, the DS-61G) forms theweld-overlay portion by the deposited metal with the composition similarto the SKD 61, and different from the welding repair, the first part 111and the second part 112 are in the state of before quenching.Accordingly, the weld bead 110 b forms the gradient metal havingextremely smooth gradient by including a heating process. Accordingly,the first part 111 and the second part 112 are combined and fastened bythe bolt 113, thus manufacturing a welded half-finished product of theinsert die 110.

Step S24 performs the heat treatment (the quenching) on thehalf-finished product of the insert die 110. By this process, the insertdie 110 has sufficient toughness and rigidity. In this respect, thefirst part 111, the second part 112, and the weld bead 110 b beforequenching are all integratedly quenched. Therefore, the weld bead 110 bhas a physical property significantly similar to the first part 111 andthe second part 112. Accordingly, a physical property boundary hardlyoccurs between the weld beads 110 b and the first part 111 and thesecond part 112 as the base material, ensuring effectively minimizingthe thermal fatigue generated caused by the boundary.

Step S25 performs a finishing process. The finishing process includesthe machining process to form the outer shape of the weld bead 110 binto a shape so as to fit the depressed portion 130 c of themovable-side main mold 130. Furthermore, the finishing process includesthe overall machining process of the outer surface and the surfacetreatment to achieve an appropriate fitting state between the insert die110 on which thermal distortion is generated and the movable-side mainmold 130. Furthermore, the finishing process includes the machiningprocess and the surface treatment to achieve the appropriate fittingstate between the fixed-side main mold 120, the movable-side main mold130, and the insert die 110.

Step S26 inspects the mold 100. This inspection includes a pressureresistance inspection, an X-ray inspection, or a similar inspection onthe cooling water passage 114. These processes allow manufacturing themold 100 having the constitution of the first embodiment.

This manufacturing process starts manufacturing the respectivecomponents of all the first part 111 and the second part 112, whichconstitute the insert die 110, from the process of the machining processon the materials, which is the SKD 61, before quenching, and afterwelding and joining the first part 111 and the second part 112, thefirst part 111 and the second part 112 are integratedly quenched.Furthermore, the welding process forms the weld-overlay portion with thedeposited metal with the composition similar to the SKD 61. Accordingly,the physical property boundary hardly occurs between the weld beads 110b and the first part 111 and the second part 112 as the base material.As a result, the thermal fatigue generated caused by the boundary can beeffectively minimized.

D. Constitution of Casting Apparatus (Spool Bush) in Second Embodiment

FIG. 6 is an explanatory view illustrating the constitution of adie-cast-casting-machine use spool bush 200 (hereinafter simply referredto as a spool bush) according the second embodiment. The spool bush 200is a component to cause the molten metal to pass through itself and topour (supply) molten metal to the mold (for example, the mold 100). Thespool bush 200 has its central axis in the vertical direction in thedrawing and has a cylindrical shape including a hollow part. The spoolbush 200 is the casting apparatus used for casting.

The spool bush 200 includes insertion liners 210, a bush body 220, outerliners 230, and a bolt 213. On the inner surfaces of the insertionliners 210, plunger holes 200 h are formed. Through the plunger hole 200h, a plunger (not illustrated), which pushes the molten metal, passes.The insertion liner 210 is a replacement component. The inner surface ofthe plunger hole 200 h is also referred to as the molten metalcontacting surface.

The spool bush 200 is constituted as follows. The bolt 213 fastens theinsertion liner 210 and the bush body 220. The outer liner 230 and thebush body 220 are permanently fastened with two weld beads 200 b 1 and200 b 2 (also referred to as welding portions). The two weld beads 200 b1 and 200 b 2 are each formed into a ring shape around the central axisof the spool bush 200.

The spool bush 200 includes cooling water passages 224 (whichcorresponds to the cooling portion in the appended claims). The coolingwater passage 224 is formed of the inner surface of the outer liner 230and a cooling groove 220 g (see FIG. 8). The cooling groove 220 g isformed on the outer diameter surface of the bush body 220. The coolingwater passages 224 are each formed into the ring shape around thecentral axis of the spool bush 200 and partially communicate with oneanother in the central axis direction of the spool bush 200. In thecooling water passage 224, the cooling water inlet (not illustrated)communicates with the cooling water discharge port (not illustrated).Accordingly, the cooling water passage 224 is constituted as acirculation path. This quickly solidifies a molten metal, allowingshortening the cycle time of casting.

The spool bush 200 is constituted such that the two weld beads 200 b 1and 200 b 2 are not exposed to the molten metal during the operation.Thus, the two weld beads 200 b 1 and 200 b 2 are not exposed to themolten metal. This allows preventing a heat cycle, which is caused bythe two weld beads 200 b 1 and 200 b 2 in contact with the molten metal.

E. Method for Manufacturing Spool Bush in Second Embodiment

FIG. 7 is a flowchart illustrating a method for manufacturing the spoolbush 200 according to the second embodiment. FIG. 8 is a process drawingillustrating the method for manufacturing the spool bush 200 accordingto the second embodiment. FIG. 9 is a process drawing illustrating anassembled state (before welding) of the bush body 220 and the outerliners 230 according to the second embodiment. To achieve theabove-described constitution, the spool bush 200 is manufactured by thefollowing method. Step S21 a performs the machining process of the bushbody 220 and the outer liners 230 (see FIG. 8). Similar to the firstembodiment, these respective components are all manufactured byperforming the machining process on materials, which is the SKD 61,before quenching.

On the inner periphery at the upper end and on the outer periphery atthe lower end of the outer liner 230, a depressed portion 230 w 1 and adepressed portion 230 w 2, which have a depressed shape for build-upwelding, are formed, respectively. On the outer periphery at the upperend and on the inner periphery at the lower end of the bush body 220, adepressed portion 220 w 1 and a depressed portion 220 w 2, which have adepressed shape for build-up welding, are formed, respectively (see FIG.9).

Step S22 a temporarily assembles the respective components 220 and 230.Specifically, Step S22 a combines the bush body 220 and the outer liners230. In this respect, the depressed portions 220 w 1 and 230 w 1 to formthe weld beads 200 b 1 (also referred to as the welding portions or theweld-overlay portions) are formed across the upper ends of the bush body220 and the outer liners 230. The depressed portions 220 w 1 and 230 w 1have a semicircular cross section. Furthermore, the depressed portions220 w 2 and 230 w 2 to form the weld beads 200 b 2 are formed across thelower portion of the bush body 220 and the lower end of the outer liner230. The depressed portions 220 w 2 and 230 w 2 have a semicircularcross section.

Step S23 a performs the heat treatment (the quenching) on the respectivecomponents 220 and 230. This embodiment performs the heat treatmentbefore the welding process in a state where the respective components220 and 230 are disassembled. This is because that, regarding the shapesof the respective components 220 and 230, performing the heat treatmentwith the respective components 220 and 230 combined results in excessiveinternal stress, which is generated by the heat treatment.

Step S24 a performs the welding process. Note that a finish machiningprocess is performed before the welding process to assemble therespective components 220 and 230. This does not cause excessiveinternal stress after the heat treatment (in the form of a product). Asdescribed above, the welding process is performed by forming the weldbeads 200 b 1 and 200 b 2 (see FIG. 6) by the TIG welding using the TIGwelding rod (for example, the DS-61G). The weld beads 200 b 1 and 200 b2 are appropriately melted into both the bush body 220 and the outerliner 230, thus constituting a gradient metal. This manufactures thehalf-finished product of the spool bush 200.

Similar to the first embodiment, Step S25 performs the finishingprocess. The finishing process includes the machining process. Themachining process forms the inner surface shape of the bush body 220into a shape so as to fit the outer surface shape of the insertion liner210, which is the replacement component. Similar to the firstembodiment, Step S26 inspects the mold 100. Step S27 inserts theinsertion liner 210 to the inside of the bush body 220, and the bolt 213fastens both.

This manufacturing process forms the weld-overlay portions at all therespective components of the bush body 220 and the outer liner 230 withthe deposited metal with the composition similar to the SKD 61. Thisensures effectively minimizing the thermal fatigue.

The die-cast-casting-machine use spool bush 200 of the second embodimentuses the cooling water passages 224 to quickly solidify the moltenmetal, thus ensuring shortening the cycle time for casting. Furthermore,without the use of an O-ring or a similar component, the weld beads 200b 1 and 200 b 2 where thermal fatigue is effectively minimized canconstitute the cooling water passages 224. This allows enhancing thedurability of the spool bush 200.

F. Constitution of Casting Apparatus (Mold) in Third Embodiment

FIG. 10A is a cross-sectional view illustrating a part of a constitutionof a mold 300 according to the third embodiment. The mold 300 has convexportions (illustrated) and internally has cooling flow passages 310,320, and 330 (which corresponds to the cooling portion in the appendedclaims). The two linear cooling flow passages 310 and 330 extendparallel toward the proximity of a product shape forming surface 300 sof the mold 300. On the other hand, the linear cooling flow passage 320communicates with both the two cooling flow passages 310 and 330.Accordingly, the three linear cooling flow passages 310, 320, and 330are mutually communicated and form a circulation path. The product shapeforming surface 300 s is also referred to as the molten metal contactingsurface.

The cooling flow passage 320 is sealed by weld beads 300 b 1 and 300 b 2at both ends. This forms columnar flow passages 320 c 1 and 300 c 2 atrespective both ends of the cooling flow passage 320. The one end of thecolumnar flow passage 320 c 1 is sealed by the weld bead 300 b 1 and theother end is coupled to the circulation path. On the other hand, the oneend of a columnar flow passage 320 c 2 is sealed by the weld bead 300 b2 and the other end is coupled to the circulation path.

The weld beads 300 b 1 and 300 b 2 seal the one ends of both thecolumnar flow passages 320 c 1 and 300 c 2. Therefore, according to theusual viewpoint of hydromechanics, this structure forms a stagnation;therefore, cooling cannot be expected. However, according to analysis ofthe inventor of this application, the following has been found. Sincethe cooling water spouts and flows in at constant cycles by evaporation(in another technical field, this has been known as a so-called pop popboat principle), this structure features high cooling capacity contraryto common sense.

G. Method for Manufacturing Mold in Third Embodiment

FIG. 10B is a process drawing illustrating a state after a machiningprocess (before welding) of the mold 300 according to the thirdembodiment. FIG. 11 is a flowchart illustrating the method formanufacturing the mold 300 according to the third embodiment. To achievethe above-described constitution, the mold 300 is manufactured by thefollowing method.

Step S31 performs a drilling process (see FIG. 10B). In this embodiment,performing the machining process on a mold base metal 350 beforequenching the SKD 61 manufactures the mold 300. A drill with a diameterof 6 mm forms three holes. The three holes include holes 310 and 330 andone through-hole 320. The two holes 310 and 330 are dug toward theproduct shape forming surface 300 s up to the proximity of the productshape forming surface 300 s. This constitution allows forming thecirculation path inside the mold 300.

The drilling process includes a boring process and a rounding process.The boring process forms the holes 310 and 330 with a drill for boring(not illustrated). The rounding process rounds most depressed portions310 c and 330 c (see FIG. 10B) of the bored holes to form rounded mostdepressed portions 310 r and 330 r (see FIG. 10A). The rounding processuses a dedicated tool whose distal end is rounded. The rounding processis performed to enhance the durability.

Step S32 performs a depressed portion forming process. The depressedportion forming process forms depressed portions 300 w 1 and 300 w 2 forbuild-up welding at both the end portions of the through-hole 320. Thedepressed portions 300 w 1 and 300 w 2 (see FIG. 10B) are formed intohemispherical depressed portions (see FIG. 10A) such that each diameterD of the weld beads 300 b 1 and 300 b 2 for build-up welding (alsoreferred to as the welding portions or the weld-overlay portions)becomes twice as large as the hole diameter, which is 12 mm in thisembodiment.

According to the analysis of the inventor of this application, thelarger the diameter D is, the larger the pressure resistance of thecooling flow passage while reduction in durability caused by weldingbecomes remarkable. Contrary, the smaller the diameter D is, the lowerthe pressure resistance of the cooling flow passage while the reductionin the durability caused by welding becomes small. Therefore, thediameters D of the weld beads 300 b 1 and 300 b 2 are the mostpreferable to be 1.5 times to twice the hole diameter viewed from theaxial directions of the columnar flow passages 320 c 1 and 300 c 2, andare also preferable to be 1 time to 2.5 times of the hole diameter.

Note that the embodiment can be achieved even outside the range. Fromthe aspect of durability, the weld beads 300 b 1 and 300 b 2 can achievesufficient cooling as long as the exposure to the molten metal isconstituted so as to be equal to or less than a predetermined ratio withrespect to areas of the weld beads 300 b 1 and 300 b 2, which constitutethe inner surfaces of the columnar flow passages 320 c 1 and 300 c 2.The predetermined ratio can be determined according to the operatingform (the temperature of molten metal and the shape of the mold).

Step S33 performs the welding process. As described above, the weldingprocess is performed by forming the weld beads 300 b 1 and 300 b 2 bythe TIG welding using the TIG welding rod (for example, the DS-61G). Theweld beads 300 b 1 and 300 b 2 are appropriately melted into the moldbase metal 350, thus constituting a gradient metal. Thus, thehalf-finished product of the mold 300 is manufactured.

Step S34 performs the heat treatment (the quenching) of thehalf-finished product of the mold 300. With this embodiment as well, aphysical property boundary hardly occurs between the weld beads 300 b 1and 300 b 2 and the mold base metal 350, ensuring effectively minimizingthe thermal fatigue, which is generated caused by the boundary.

Step S35 performs the finishing process. Step S36 inspects the mold 300.This inspection includes the pressure resistance inspection, the X-rayinspection, or a similar inspection on the cooling flow passages 310,320, and 330. These processes can manufacture the mold 300 having theconstitution of the third embodiment.

According to this manufacturing process, similar to the first embodimentand the second embodiment, the physical property boundary hardly occursbetween the weld beads 300 b 1 and 300 b 2 and the mold base metal 350.Furthermore, since the cooling water spouts and flows in at constantcycles in the columnar flow passages 320 c 1 and 300 c 2 by evaporation,the weld beads 300 b 1 and 300 b 2 can be effectively cooled.Additionally, it is constituted such that the exposure of the weld beads300 b 1 and 300 b 2 to the molten metal becomes equal to or less thanthe predetermined ratio with respect to the areas of the weld beads 300b 1 and 300 b 2, which constitute the inner surfaces of the columnarflow passages 320 c 1 and 300 c 2, to ensure sufficiently cooling. As aresult, the thermal fatigue generated caused by the boundary with theweld beads 300 b 1 and 300 b 2 can be effectively minimized.

H. Modification

In the above-described embodiment, this build-up welding is formed bythe TIG welding using the TIG welding rod; however, another weldingmethod may be employed. Note that since the TIG welding can obtainbeautiful, high-quality weld beads (weld-overlay portions) and thereforeis preferable in terms of allowing application to welding of variousmetals.

The casting apparatus may be constituted as follows. The castingapparatus has a plurality of components including a welding componenthaving the welding portion. With the plurality of components assembled,the welding portion is constituted not to be exposed to the moltenmetal.

The casting apparatus may be constituted as follows. The castingapparatus is a mold. The molten metal contacting surface constitutes apart of the mold as a product shape forming surface. The product shapeforming surface forms a shape of the cast product set in advance. Anouter surface of the welding portion is constituted so as not to beexposed to the molten metal by contact with any of outer surfaces of theplurality of components.

The casting apparatus may be constituted as follows. The cooling portionis manufactured by welding a material before quenching and subsequentlyquenching the material.

The casting apparatus may be constituted as follows. The castingapparatus is a mold. The cooling flow passage includes a columnar flowpassage. One end of the columnar flow passage is sealed by the weldingportion. Another end of the columnar flow passage communicates with acirculation path. The circulation path causes a cooling medium tocirculate. The welding portion has a diameter 1.5 times to 2.5 times ofa diameter of the columnar flow passage viewed from an axial directionof the columnar flow passage such that the diameter becomes equal to orless than the predetermined ratio.

The casting apparatus may be constituted as follows. A length of thecolumnar flow passage from the one end to the other end is longer thanthe diameter of the columnar flow passage.

The casting apparatus may be constituted as follows. The castingapparatus is a sprue bushing. The molten metal contacting surfaceconstitutes a path to cause the molten metal to pass through to supplythe molten metal to the mold.

The casting apparatus may be constituted as follows. The columnar flowpassage is a mold whose length from the one end to the other end islonger than the diameter of the columnar flow passage.

While one or more embodiments of the present invention seals the coolingflow passage by the welding process, the reduction in durability of thecasting apparatus caused by the welding process can be minimized.

What is claimed is:
 1. A casting apparatus for manufacturing a castproduct from molten metal, the casting apparatus comprising: a moltenmetal contacting surface for contact with the molten metal; and acooling portion forming a cooling flow passage, the cooling flow passagebeing configured to cool the molten metal contacting surface, wherein atleast a part of an inner surface of the cooling flow passage isconstituted of a welding portion formed by welding, the welding portionsealing the cooling flow passage, and the welding portion is constitutedsuch that an exposure to the molten metal becomes equal to or less thana predetermined ratio with respect to an area of the welding portionconstituting the inner surface of the cooling flow passage.
 2. Thecasting apparatus according to claim 1, wherein the casting apparatushas a plurality of components including a welding component having thewelding portion, and with the plurality of components assembled, thewelding portion is constituted not to be exposed to the molten metal. 3.The casting apparatus according to claim 2, wherein the castingapparatus is a mold, the molten metal contacting surface constitutes apart of the mold as a product shape forming surface, the product shapeforming surface forming a shape of the cast product set in advance, andan outer surface of the welding portion is constituted so as not to beexposed to the molten metal by contact with any of outer surfaces of theplurality of components.
 4. The casting apparatus according to claim 1,wherein the cooling portion is manufactured by welding a material beforequenching and subsequently quenching the material.
 5. The castingapparatus according to claim 1, wherein the casting apparatus is a mold,the cooling flow passage includes a columnar flow passage, one end ofthe columnar flow passage being sealed by the welding portion, anotherend of the columnar flow passage communicating with a circulation path,the circulation path causing a cooling medium to circulate, and thewelding portion has a diameter 1.5 times to 2.5 times of a diameter ofthe columnar flow passage viewed from an axial direction of the columnarflow passage such that the diameter becomes equal to or less than thepredetermined ratio.
 6. The casting apparatus according to claim 5,wherein the columnar flow passage is a mold whose length from the oneend to the other end is longer than the diameter of the columnar flowpassage.
 7. The casting apparatus according to claim 1, wherein thecasting apparatus is a sprue bushing, and the molten metal contactingsurface constitutes a path to cause the molten metal to pass through tosupply the molten metal to a mold.
 8. A method for manufacturing acasting apparatus for manufacturing a cast product from molten metal,the method comprising: providing a molten metal contacting surface forcontact with the molten metal and a material before quenching, a part ofa cooling flow passage being formed at the material, the cooling flowpassage being configured to cool the molten metal contacting surface,wherein welding at least a part of an inner surface of the cooling flowpassage to form a welding portion configured to seal the cooling flowpassage, and the welding portion is constituted such that an exposure tothe molten metal becomes equal to or less than a predetermined ratiowith respect to an area of the welding portion constituting the innersurface of the cooling flow passage.
 9. The casting apparatus accordingto claim 2, wherein the cooling portion is manufactured by welding amaterial before quenching and subsequently quenching the material. 10.The casting apparatus according to claim 3, wherein the cooling portionis manufactured by welding a material before quenching and subsequentlyquenching the material.